Pollution control for foundry cupolas is a major problem. The open charge doors, used with conventional iron-melting cupolas, allow untreated gases to escape through the opening, contributing to the pollution problem. These charge doors are located on a side of an upper exhaust gas stack, and are used to introduce ferrous materials, coke, and limestone into the burden of the cupola. The open charge door allows the introduction of large amounts of ventilating air into the exhaust gases of the cupola which must be treated before release to the atmosphere. The pollution control equipment used to treat these exhaust gases must be large enough to accommodate this large amount of ventilating air.
Poor mixing of the incoming ventilating air with the exhaust gases also often causes intermittent small explosions known as "puffing". "Puffing" causes untreated gases to escape into the atmosphere through the open charging door. In addition, when conventional vibratory feeders are used to add charge materials through the open charge door of these conventional cupolas, the charge materials deflect part of the cupola exhaust gases outwardly through the open charge door. Untreated gases that escape through the open charge door are known as "fugitive emissions" because these gases bypass the pollution control equipment provided to treat the exhaust gases exiting the stack.
One method of solving the pollution problem associated with open charge doors is to use a feeding device which delivers the charge to the furnace through the charge door with apparatus for providing a positive air pressure outside the charge door. This positive pressure prevents the exhaust gases from exiting to the atmosphere through the charge door. U.S. Pat. No. 3,633,897 to Vogel illustrates this method.
Another source of pollution with conventional foundry cupolas is the melting process itself. With a vibratory feeder method of charging, the melting process is adversely affected as large, heavy pieces of incoming material tend to drop to a side of the cupola opposite the charge door, while small pieces tend to drop toward the side just below the charge door. A cupola burden formed in this way is detrimental to the efficient operation of the cupola. Process gases are diverted to a side of the cupola opposite the charge door since these gases pass more readily through the larger voids that exist between large pieces than through the smaller voids that exist between small pieces. In such a conventional cupola, a disproportionately large amount of the off-gases pass through the burden opposite the charge door, while a large proportion of the process heat is lost through the wall opposite the charging door.
What is needed is a device for introducing charging materials into a foundry cupola through a charge door without the need for providing positive air pressure outside the charge door. Further, a device is needed which promotes the complete combustion of combustible off-gases, and improves the thermal efficiency of the melting process to reduce the consumption of coke. What is needed is a device that distributes the incoming charge of ferrous materials, coke and limestone evenly around the periphery of the cupola, where the large pieces are deposited mainly in the center of the cupola, and the smaller pieces are deposited mainly toward the outside. This segregation of materials by size improves the thermal efficiency of the process by keeping the hot gases rising in the center of the burden, imparting more heat to the charging materials and reducing heat losses through the cupola wall. In addition, the device needs to restrict incoming ventilating air to a minimum and mix the necessary combustion air with the off-gases for complete and even combustion of combustible components.